U.S. patent number 6,510,929 [Application Number 09/722,613] was granted by the patent office on 2003-01-28 for controllable magneto-rheological fluid damper.
This patent grant is currently assigned to The Board of Regents of the University and Community College System of Nevada. Invention is credited to Everet O. Ericksen, Faramarz Gordaninejad.
United States Patent |
6,510,929 |
Gordaninejad , et
al. |
January 28, 2003 |
Controllable magneto-rheological fluid damper
Abstract
A damper includes a housing, a piston, and a magneto-rheological
(MR) fluid. The piston is movably disposed within the housing such
that the piston divides an interior of the housing into first and
second cavities and a passage defined in the piston couples the
first and second cavities. The passage includes at least a disk
shape space within the piston defined between by two substantially
parallel surfaces. The MR fluid damps motion of the piston by a
flow of MR fluid through the passage, and a magnet produces a
magnetic field within at least the disk shape space of the
passage.
Inventors: |
Gordaninejad; Faramarz (Reno,
NV), Ericksen; Everet O. (Newport, MI) |
Assignee: |
The Board of Regents of the
University and Community College System of Nevada (Reno,
NV)
|
Family
ID: |
26863620 |
Appl.
No.: |
09/722,613 |
Filed: |
November 28, 2000 |
Current U.S.
Class: |
188/267.2;
188/320; 267/140.14 |
Current CPC
Class: |
F16F
9/535 (20130101) |
Current International
Class: |
F16F
9/53 (20060101); F16F 009/53 () |
Field of
Search: |
;188/267.2,267.1,267,314,316,320 ;267/64.15,140.14,217 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Schwartz; Christopher P.
Assistant Examiner: Nguyen; Xuan Lan
Attorney, Agent or Firm: Morgan, Lewis & Bockius LLP
Parent Case Text
This application claims priority to a provisional application, Ser.
No. 60/167,933, filed Nov. 29, 1999.
Claims
What is claimed is:
1. A damper, comprising: a housing; a piston movably disposed
within the housing, the piston dividing an interior of the housing
into first and second cavities and having a passage defined in the
piston to couple the first and second cavities, wherein the passage
includes at least a disk shaped space within the piston defined by
an entire region between two substantially parallel surfaces within
a radial distance from an axis of the piston, a plurality of inlet
flow ports coupling the first cavity to radially outer portions of
the disk shaped space each through a substantially straight path,
and a plurality of outlet flow ports each coupling the second
cavity with a central portion of the disk shaped space; a
magneto-rheological (MR) fluid contained within at least the first
cavity and the disk shaped space such that the MR fluid completely
fills the entire region between the two substantially parallel
surfaces within the radial distance from the axis of the piston,
motion of the piston being damped by a flow of MR fluid through the
passage; a magnet disposed to produce a magnetic field within at
least the disk shape space of the passage.
2. The damper according to claim 1, wherein the plurality of inlet
flow ports are disposed proximate the radial edge of the
piston.
3. The damper according to claim 1, wherein the plurality of outlet
flow ports includes a portion defined along an axis of the piston
and a portion opening to the second cavity.
4. The damper according to claim 1, wherein the piston includes a
shaft portion.
5. The damper according to claim 1, wherein the magnet is an
electromagnet.
6. The damper according to claim 1, wherein the number of inlet
ports and the number of outlet ports being different.
7. The damper according to claim 1, wherein the magnet is disposed
on the piston within the housing.
8. A damper, comprising: a housing; a piston movably disposed
within the housing, the piston dividing an interior of the housing
into first and second cavities and having a passage defined in the
piston to couple the first and second cavities, wherein the passage
includes at least a space within the piston coupled with the first
cavity through a plurality of substantially straight inlet flow
ports and coupled with the second cavity through a plurality of
outlet flow ports with the number of inlet flow ports being
different than the number of outlet flow ports; a
magneto-rheological (MR) fluid contained within at least the first
cavity, motion of the piston being damped by a flow of MR fluid
through the passage; a magnet disposed to produce a magnetic field
within at least a portion of the passage.
9. The damper according to claim 8, wherein the plurality of inlet
flow ports of the passage are disposed proximate the radial edge of
the piston.
10. The damper according to claim 8, wherein the passage includes a
portion defined along an axis of the piston to couple the space
with the second cavity in conjunction with the at least one outlet
flow port.
11. The damper according to claim 8, wherein the piston includes a
shaft portion.
12. The damper according to claim 8, wherein the magnet is an
electromagnet.
13. The damper according to claim 8, wherein the magnet produces a
magnetic field within at least the space.
14. A damper, comprising: a housing; a piston movably disposed
within the housing, the piston dividing an interior of the housing
into first and second cavities and having a passage defined in the
piston to couple the first and second cavities, wherein the passage
includes a plurality of substantially straight inlet ports to
couple the passage with the first cavity and a plurality of outlet
ports to couple the passage with the second cavity, the number of
inlet flow ports being different than the number of outlet flow
ports; a magneto-rheological (MR) fluid contained within at least
the first cavity, motion of the piston being damped by a flow of MR
fluid through the passage; a magnet disposed to produce a magnetic
field within at least a portion of the passage.
15. The damper according to claim 14, wherein the inlet flow ports
are disposed proximate the radial edge of the piston.
16. The damper according to claim 15, wherein the inlet flow ports
are disposed randomly.
17. The damper according to claim 14, wherein the inlet flow ports
are disposed randomly.
18. The damper according to claim 14, wherein the outlet flow port
are further coupled with a portion of the passage defined along an
axis of the piston.
19. The damper according to claim 14, wherein the magnet is an
electromagnet.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a damper, and more particularly,
to a controllable magneto-rheological fluid damper.
2. Discussion of the Related Art
During the past decade, there has been increasing interest in the
development of controllable shock absorbers that utilize
electro-rheological fluid (ERF) and magneto-rheological fluid
(MRF). The possibility of using ERF or MRF based damping devices in
various applications has made these controllable devices attractive
to the vibration control field. Controllable shock absorbers can
potentially be used in a variety of mechanical systems such as
bicycles, motorcycles, automobiles, trucks, ships, trains,
airplanes, bridges, buildings and/or other structures, sports
equipment and any other systems using vibration control.
An MRF consists of micron-sized, magnetically polarized particles
suspended in a carrier fluid such as silicon or mineral oils. MRFs
are capable of responding to a magnetic field in a few
milliseconds. The material properties of an MRF can be changed
rapidly by increasing or decreasing the intensity of the applied
magnetic field. This is realized as a controllable increase in the
apparent viscosity of the fluid by varying the current supplied to
the damper's built-in electromagnet. A higher fluid viscosity
yields a higher damping force. This is the mechanism behind the
controllability of MRF dampers.
In a conventional MRF damper disclosed by FIG. 9(c) of U.S. Pat.
No. 5,277,281, the system uses an entrance fluid port and a exit
fluid port connected by a channel. The fluid flows through a
lateral channel portion in the path between the entrance and exit
ports. Here, the lateral channel portion extends through a fixed
arc. In addition, the lateral channel is required to flow around a
plug, associated with the shaft, that extends into the center of
the piston.
As a result of this design, the above-referenced damper suffers
from a number of limitations. For example, the damper cannot
accommodate multiple entrance and exit ports. The use of a single
entrance and a single exit port diminishes the flexibility of the
design with respect to the damping force that can be generated.
This is of particular importance when small initial or zero-field
(no current applied) damping forces are desired. In addition, the
MR fluid must flow around the plug in the center of the piston,
thereby reducing the surface area to which the MR fluid chains
adhere to the wall. This reduction in surface area reduces the
damping force that can be generated by the MR fluid upon
application of a magnetic field.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a damper that
substantially obviates one or more of the problems due to
limitations and disadvantages of the related art.
An object of the present invention is to provide a damper that has
improved damping characteristics.
Another object of the present invention is to provide of a damper
that can be efficiently manufactured at a low cost.
Additional features and advantages of the invention will be set
forth in the description which follows, and in part will be
apparent from the description, or may be learned by practice of the
invention. The objectives and other advantages of the invention
will be realized and attained by the structure particularly pointed
out in the written description and claims hereof as well as the
appended drawings.
To achieve these and other advantages and in accordance with the
purpose of the present invention, as embodied and broadly
described, a damper comprises a housing; a piston movably disposed
within the housing, the piston dividing an interior of the housing
into first and second cavities and having a passage defined in the
piston to couple the first and second cavities, wherein the passage
includes at least a disk shape space within the piston defined
between by two substantially parallel surfaces; a
magneto-rheological (MR) fluid contained within at least the first
cavity, motion of the piston being damped by a flow of MR fluid
through the passage; a magnet disposed to produce a magnetic field
within at least the disk shape space of the passage.
In another aspect, a damper comprises a housing; a piston movably
disposed within the housing, the piston dividing an interior of the
housing into first and second cavities and having a passage defined
in the piston to couple the first and second cavities, wherein the
passage includes at least a space within the piston coupled with
the first cavity through a plurality of inlet flow ports and
coupled with the second cavity through at least one outlet flow
port; a magneto-rheological (MR) fluid contained within at least
the first cavity, motion of the piston being damped by a flow of MR
fluid through the passage; a magnet disposed to produce a magnetic
field within at a portion of the passage.
In another aspect, a damper comprises a housing; a piston movably
disposed within the housing, the piston dividing an interior of the
housing into first and second cavities and having a passage defined
in the piston to couple the first and second cavities, wherein the
passage includes a plurality of inlet ports to couple the passage
with the first cavity and a plurality of outlet ports to couple the
passage with the second cavity, the number of inlet flow ports
being different than the number of outlet flow ports; a
magneto-rheological (MR) fluid contained within at least the first
cavity, motion of the piston being damped by a flow of MR fluid
through the passage; a magnet disposed to produce a magnetic field
within at least a portion of the passage.
It is to be understood that both the foregoing general description
and the following detailed description are exemplary and
explanatory and are intended to provide further explanation of the
invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are included to provide a further
understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and together with the description serve to explain
the principles of the invention. In the drawings:
FIG. 1 is a cross-section view of an MRF vibration damper according
to an embodiment according to the present invention;
FIG. 2 is an enlarged, cross-sectional view of the piston of the
damper of FIG. 1;
FIG. 3 is a cross-sectional view of the damper across line III--III
of FIG. 1;
FIG. 4 is a cross-sectional view of the damper across line IV--IV
of FIG. 1; and
FIG. 5 is a graph of the experimental force-displacement results a
damper according to the embodiment of the damper of FIG. 1 with
test conditions at a frequency of 1 Hz and a peak-to-peak
displacement of 0.2 in (0.508 cm).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present application is related to and claims the benefit of
U.S. Provisional Patent Application No. 60/167,933 entitled
"Controllable Magneto-Rheological Fluid Shock Absorbers" filed Nov.
29, 1999 by the present inventors, which is hereby incorporated by
reference.
Reference will now be made in detail to the preferred embodiments
of the present invention, examples of which are illustrated in the
accompanying drawings.
The present invention relates to an MRF damper. As will be
generally described and will be described in detail below, the
damper preferably comprises one or more housings each containing a
piston. The piston is generally cylindrical in shape and is movable
within an interior of the housing to define first and second
interior portions. The housing contains an appropriate amount of
MRF. The material properties of the MRF are varied using magnetic
fields (generally cylindrical or torroidal in shape) that surround
and incorporate the regions of the housing and piston. A variable
magnetic field is generated by winding a coil of magnetic wire
around the housing. Alternatively, the coil can be wound around a
portion of the housing having the piston and the corresponding MRF
passages. Seals are provided at the caps of the housing by O-rings
or other suitable means to prevent leakage and/or reduce
contamination. A spring or spring-like materials can be employed in
series or parallel to construct a spring-dashpot damping
device.
The present invention takes advantage of the fact that the ferrous
particles in MRF form chain-like strings along the flux lines. The
chain-like formation of ferrous particles (MRF build-up) through
the passage provides an effective increase in apparent viscosity of
the fluid within the MRF flow passages, thereby increasing the
pressure drop across the two ends of the piston. The increase in
pressure drop across the two ends of the piston increases the
resisting (damping) force.
According to the present invention, a portion of the MR fluid flow
is occurs in a disk shaped void (space) defined between two
parallel surfaces incorporated in the MRF damper. With this type of
arrangement, the contact area for the chain-like formation of
ferrous particles to adhere to the wall is significantly increased.
That is, the MR fluid flow is distributed about a larger area,
thereby enabling the MRF chains be formed within the larger area
having a reduced MRF flow density. Furthermore, this design
incorporates multiple inlet and outlet flow ports allowing for
separate compression and rebound flow paths. This allows the damper
to produce different compression and rebound force characteristics
if desired. Furthermore, multiple inlet and outlet flow paths
provide greater flexibility in the design of the dampers. The
number of inlet and outlet flow paths can be varied in order to
produce a desired off-state (zero applied magnetic field) damping
force. The number of inlet ports need not be the same as the number
of outlet ports.
Specific embodiments of the damper of the present invention will
now be described in detail with reference to FIGS. 1-5.
FIG. 1 illustrates the MRF vibration damper which includes a
housing 3 and a piston 6 that divides the interior of the cylinder
3 into two portions: the compression chamber 7 and the rebound
chamber 5. Incorporated into the piston 6 in the embodiment of FIG.
1 is a wound magnetic coil 10. The coil 10 has two external
electrical wire leads 4 that are connected to an external
electrical power source. There are two external mounting pieces 1
and 9 to secure the movable end (comprising mount 1, piston rod 2,
and piston 6) of the damper and the non-movable end 9 to the
vehicle. The accumulator passage 8 accommodates the added volume
due to the rod 2 when the piston 6 is compressed.
FIG. 2 shows a enlarged cross-sectional view of the MRF damper of
FIG. 1 to illustrate the internal elements of the damper. The
piston 6 may have one or more inlet ports 11. The fluid enters the
parallel plate flow region 12 and converges to the center of the
piston 6. The flow region 12 is the primary location of the "MRF
build-up". The MR fluid flows through the center of the rod 13 and
exits through one or more exit ports 14.
FIG. 3 shows a top, cross-sectional view of the damper across line
IlI--III of FIGS. 1 and 2. As shown, there are four exit flow ports
14 and one flow port 13 through the center of the rod 2. Other
numbers of exit flow ports 14 may be used so long as there are one
or more.
FIG. 4 shows a top, cross-sectional view of the damper across line
IV--IV in FIGS. 1 and 2. As shown, there are six inlet flow ports
11 in the piston 6. However, other numbers of inlet flow ports 11
can be used so long as there are one or more. Although FIG. 4 shows
the six inlet flow ports regularly arranged to define a hexagonal
pattern, the inlet flow ports may be arranged in any patter
including random patterns.
A damper in accordance with FIGS. 1--4 was built and tested in the
laboratory. FIG. 5 shows the force vs. displacement performance
test of the proposed MRF shock absorber design at three different
input currents: 0 A, 1 A, and 2 A. The plot shows the response of
the damper to a displacement input of 0.2 inches (0.508 cm)
(peak-to-peak) and a frequency of 1.0 Hz. As can be seen in FIG. 5,
after activating the MRF damper with 2 amps of input current, the
maximum force produced by the damper increases from 5 lbf (22.24 N)
to 235 lbf (1045 N). This is an increase of 230 lbs. (1022.76 N)
from 0.0 amp to 2.0 amp current input. In addition, a damper was
tested in off-road applications on a motorcycle and found to
provide superior performance.
As described above, the damper according to the present invention
provides a MR fluid flow channel having a portion defined as a disk
shaped void between parallel surfaces, thereby resulting in
parallel plate flow. In a preferred embodiment, the MR fluid enters
the piston through multiple inlets at the outer most radial edge of
the piston. The fluid flows through a disk shaped void defined
between parallel surfaces towards the axial center of the piston.
Then, in the preferred embodiment, the fluid flows through a
passage through the center of the piston or rod and subsequently
exits. Because the rod does not extend to the center of the piston
(i.e., where the disk shaped void is defined), the contact area on
which the MR fluid forms chains to the surface of the wall is
increased in the damper. Thus, much higher damping forces result
from the magnetic field, thereby leading to higher damping forces
of the damper. Also, as mentioned above, a single or multiple inlet
ports can be utilized allowing for greater flexibility in the
design. With the multiple inlet and outlet port design, it is
possible to design separate compression and rebound flow paths
resulting in different compression and rebound force
characteristics.
As described herein, the damper of the present invention provides
variably controlled flow of MR fluid in passages therein.
Accordingly, the damper has improved performance characteristics.
For example, the MR fluid flow path includes a disk shaped void
defined between parallel surfaces, thereby causing a parallel plate
flow. The parallel plate flow arrangement increases the contact
area on which the MR fluid forms chains from the surface of the
wall. The result is much higher damping force induced by the
magnetic field. In addition, the design permits multiple inlet and
outlet flow ports, thereby allowing for separate compression and
rebound flow paths. Thus, the damper can achieve different
compression and rebound force characteristics if desired. Also,
multiple inlets and outlets give greater flexibility in the design
of the damping forces by varying the number inlet and outlet flow
ports.
In accordance with the embodiments described above, a number of
variations can be realized in accordance with the specific
application. For example, the housings of the dampers may comprise
one or more of cavity units for containing MR fluid. In addition,
The cavity units may be formed of either non-ferrous or ferrous
materials or a combination of both types of materials. The dampers
devices may also comprise one or more piston units that move within
a cavity to define and displace MR fluid from multiple cavity
portions. Similarly, the piston(s) may be manufactured from a
combination of ferrous or non-ferrous materials. While the above
described embodiments have one or more solenoids formed of windings
of wires (electromagnets) to generate a magnetic field in and
around the piston(s), other magnet types or techniques can be used
to produce a magnetic field in accordance with the present
invention. For example, the use of permanent magnets in place of,
or in conjunction with, electromagnets may be used. Additionally,
the use of an electromagnet to counteract the constant magnetic
field of a permanent magnet(s) can be used to produce a reverse
controlled mode. As another example, while axial piston motion has
been described above, other motions, such as rotary motion or
combinations of linear and rotary motions, can be applied in the
damper of the present invention. Further, the design need not be
limited to only two cavities, since the design may comprise a
plurality of independent and/or dependent MR fluid cavities
extending in any direction or dimension.
It will be apparent to those skilled in the art that various
modifications and variations can be made in the damper of the
present invention without departing from the spirit or scope of the
invention. Thus, it is intended that the present invention cover
the modifications and variations of this invention provided they
come within the scope of the appended claims and their
equivalents.
* * * * *